Golfers are frequently interested in knowing their distance and direction to the pin from the tee or fairway locations. Skilled golfers, and in particular professionals, can control their shots to within a few yards of a desired target. Thus it is of considerable advantage to this class of golfers to be able to estimate their distance to the pin or other locations with very high accuracy from any feasible position of play. This is also true for the average or weekend golfer who does not have the experience to estimate the distance to a particular hole with any degree of accuracy.
Previous systems have relied on optical sighting systems, dead-reckoning systems, and RF-based systems. In a system to Woodward (U.S. Pat. No. 3,868,692), a transmitter placed at each pin broadcasts a continuous wave RF signal. A hand-held unit measures the field-strength of the signal emitted by each pin and uses an analog meter to indicate yardage to the pin. This system is straightforward and simple, and allows the plurality of hand-held units to operate on a non-interfering basis, but requires the golfer to visually estimate yardage from an analog meter on the hand-held unit. Accuracy can also be affected significantly by analog component tolerances and aging, as well as low levels of unexpected RF interference at the transmitter frequencies. In a system to Henriques and Angleman (U.S. Pat. No. 4,297,701), a hand-held transceiver unit transmits a coded signal to a flagstick mounted unit which is itself a transceiver. The flagstick unit is identified by the code, and the identified flagstick unit retransmits the received signal back to the hand-held unit. Distance estimation is based on measuring the two-way signal delay between the hand-held and flagstick units, which is implemented in the hand-held unit by charging and discharging of a capacitor. These systems also suffer from the necessity of mounting the transmitter or transceiver unit on or near the flagstick, where it may be easily damaged and is undesirable aesthetically, or may not be permitted.
Other patents for distance determination, such as Cockerell (U.S. Pat. No. 4,698,781) and Storms et al (U.S. Pat. No. 4,703,444) describe a system in which hand-held transceivers operate in conjunction with a triangular arrangement of fixed-position transceivers which eliminate the need for flag-pole mounted units. Each hand-held interrogation unit stores the coordinates of key course features and the fixed-position transceivers and can provide the golfer with an estimate of his distance to any of these features on a particular hole. In the system to Storms et al, three remote transmitters arranged approximately in a triangle about a golf course transmit repetitive pulse sequences which are received and processed by the hand-held interrogation unit. The hand-held unit uses a counter to estimate the difference in arrival time between the pulse transmitted by the first and second transmitters, and then the arrival time difference between the pulses from the second and third transmitters. Based on these two time-difference estimates, the hand-held unit computes its current location and then computes and displays the distance to the desired course feature.